Steady rests for supporting central workpiece regions during the machining of central and/or eccentric workpiece regions, in particular bearing points on, in particular, crankshafts, are known. These steady rests serve the purpose of additionally supporting so-called relatively soft workpieces, such as crankshafts, while they are being ground, so that the application of the grinding forces leads, if possible, to no deformation of the workpiece that is to be ground or at least causes only a minor deformation to occur.
Steady rests from the AROBOTECH Company, which are preferably used for shaft diameters or main bearing diameters of crankshafts of, for example, up to 70-80 mm, are often used on grinding machines for grinding crankshafts. In the case of larger shaft parts or crankshafts, for which steady rests must be used for grinding, the known steady rests are disadvantageous insofar as they usually require a large space. Because of their design, these known steady rests with their steady rest jaws must be retracted when the workpieces are loaded and unloaded. These known steady rests usually have three jaws, which usually have a PCD (polycrystalline diamond) coating or CBN (cubic boron nitride) coating. By way of this design, the respective bearing point that is to be supported is firmly “clamped” by three jaws, with the bearing points being supported between the PCD-coated supporting elements in a diameter range greater than 180°, e.g., about 210°. The workpiece is “clamped” in a self-centering way and the advance of the jaws takes place toward the workpiece center, i.e., centrically with respect to the bearing diameter. The motions of the individual steady rest jaws are permanently mechanically coupled, which leads to a relatively complicated mechanical system. The “clamping” at three fixed points requires a previously well pre-machined bearing point for placement of the steady rest. It is therefore difficult to adjust the steady rest for the aforesaid reasons. The permanent mechanical coupling of the three jaws of the known steady rest requires relatively big forces to be transferred when it is put in place, which leads to pronounced track marks at the bearing point that is to be supported. It is, in particular, known that so-called two-point steady rests should be used for workpieces having larger diameters, with the two independently adjustable, possibly PCD-coated supports supporting the workpiece being respectively adjusted by means of separate CNC shafts. The use of two separate CNC shafts increases the construction complexity of such steady rests and thus their costs, which is why such steady rests are technically very complex and very expensive. The two support points and/or regions of such known steady rests are usually positioned at right angles to each other, with one support point and/or region being positioned at the bearing point from below and the other support point and/or region opposite the grinding wheel and being placed against the bearing point.
Steady rests where the two bearing points are arranged in a positively controlled way as in U.S. Pat. No. 6,257,972 B1, with support being provided by a third, opposite beating point, are also known. The individual steady rest supporting components are either set by means of stops or are installed at a fully polished bearing point. No adjustment of the steady rest when the steady rest position is ground is or can be provided for.
A two-point steady rest with two fixed, mutually opposite supporting parts is moreover known from DE 10 2011 015 205 B3. This known steady rest for supporting a workpiece horizontally and vertically has two supports disposed at a lateral distance from each other that are adjustable with respect to the workpiece, with a conveyor that is loosely guided by a base carrying the supports and the conveyor being displaceable in a radial direction with respect to the workpiece, so that both supports can be jointly delivered to the workpiece. The radial displacement of the conveyor takes place against the effect of a spring, so that an additional movable member is present between the workpiece that is to be supported and the actual steady rest supporting base. The maximum attainable concentricity is therefore on the order of a few μm.